Vitamin D levels after UVB radiation: effects by UVA additions in a randomized controlled trial

BackgroundUltraviolet B (UVB) radiation increases the serum level of 25-hydroxyvitamin D [25(OH)D]. However, the impact of UVA on vitamin D synthesis by UVB is poorly understood clinically. ObjectiveTo examine how different combinations of UVA and UVB radiation affect S-25(OH)D for the same vitamin D-weighted exposure. Materials and MethodsHealthy participants were recruited and subsequently divided into four comparable groups regarding initial 25(OH)D value. The different radiations given were whole-body UVB (n=23), UVAB (n=23) and UVA (n=10). The controls (n=19) had no intervention. The exposure times were chosen to give the same calculated vitamin D effective dose (suberythemal exposures 1 standard erythema dose). Blood samples were collected before the first irradiation (t0), immediately after the last (fifth) irradiation (t1) and then after another 2 days after the last (fifth) irradiation (t2). ResultsUVB and UVAB radiation significantly increased 25(OH)D levels. In the UVA group the increase was less with the same vitamin D-weighted radiation dose. ConclusionsShort sessions of UVB or UVAB radiation with the same vitamin D-weighted exposure increased 25(OH)D levels. The UVA dose does not influence 25(OH)D levels under short exposure times. However, there was a significantly lower increase of 25(OH)D levels during longer UVA irradiation (9min).